In recent years, developments of house-service robots such as pet robots or the like have been vigorously carried out, and it has been expected that in the future, more practical house-service robots, such as house-keeping support robots and the like, will be put into practical use. Since the house-service robot is used in a home, and needs to live together with people, its required specifications are made different from those of a conventional industrial robot.
In the case of the industrial robot, electric motors or speed reducers are used, and a high hand position precision, such as a repetitive precision of 0.1 mm or the like, has been achieved by a feed-back controlling operation with a high gain. However, such a mechanism driven by electric motors is high in rigidity, and tends to lack flexibility in most cases, resulting in an issue with safety.
In contrast, in the case of the house-service robot, such high precision with a repetitive precision of 0.1 mm or the like is not necessarily required, and more emphasis is placed on safety, that is, on such a characteristic as not to cause damage even in contact with a person. Therefore, the mechanism to be driven by electric motors, such as that of a conventional industrial robot, is not considered to be suitable for the field in which more emphasis is placed on safety, such as the field of the house-service robots, and flexible and safe robot arms are required.
In view of these issues, for example, a robot arm which utilizes a pneumatic actuator of McKibben type has been proposed. The McKibben type pneumatic actuator has a structure in which regulating means formed by fiber cords is placed on an outer surface of a tube-shaped elastic member made of a rubber material, with the two ends of the tube-shaped elastic member being air-tightly sealed with a sealing member. When an inner pressure is applied to the inner space of the tube-shaped elastic member by a compressive fluid such as air through fluid injection and discharge means, the tube-shaped elastic member tries to expand mainly in a radial direction; however, the expansion is converted to a motion in a center axis direction of the tube-shaped elastic member by the regulating means so that the overall length thereof is contracted. Since the actuator of the McKibben type is mainly composed of an elastic member, it is flexible and makes it possible to form a safe actuator having a light weight.
However, the fluid-pressure drive actuator, such as the actuator of the McKibben type, which is operated by a fluid pressure such as air, is poor in response characteristic due to influences of elastic characteristics caused by the compressive fluid, flow passage resistance, or the like. For this reason, the elastic body actuator has issues in that, for example, it is not possible to achieve a desired precision by using a conventional generally-used feed-back controlling operation.
In view of these issues, as a conventional technique, a control device has been disclosed (Patent Document 1) in which inner-state error compensation means is installed so that a control system for feeding back the inner state of the elastic body actuator is prepared, and desired inner-state determination means is also installed so that a control system for feeding forward a desired inner state is prepared; thus, the resulting control device makes it possible to carry out a high-speed controlling operation with high precision, and improved responsiveness, with little stationary error.